Methods of forming rutile titanium dioxide and associated methods of forming semiconductor structures

ABSTRACT

Methods of forming rutile titanium dioxide. The method comprises exposing a transition metal (such as V, Cr, W, Mn, Ru, Os, Rh, Ir, Pt, Ge, Sn, or Pb) to oxygen gas (O 2 ) to oxidize the transition metal. Rutile titanium dioxide is formed over the oxidized transition metal. The rutile titanium dioxide is formed by atomic layer deposition by introducing a gaseous titanium halide precursor and water to the oxidized transition metal. Methods of forming semiconductor structures having rutile titanium dioxide are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to U.S. patent application Ser. No.13/021,910, filed on Feb. 7, 2011, and titled “CAPACITORS INCLUDING ARUTILE TITANIUM DIOXIDE MATERIAL AND SEMICONDUCTOR DEVICES INCORPORATINGSAME,” now U.S. Pat. No. 8,564,095, issued Oct. 22, 2013, the disclosureof which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

Embodiments of the present disclosure relate to semiconductor devicefabrication and, more specifically, to methods of forming rutiletitanium oxide on a semiconductor structure, and to methods of formingsemiconductor device structures including the rutile titanium oxide.

BACKGROUND

As conventional semiconductor memory devices, such as Flash memory anddynamic random access memory (DRAM), reach their scaling limits,research has focused on commercially viable low power, low operationvoltage, high-speed, and high-density non-volatile memory devices.Materials having high dielectric constants (i.e., high static relativepermittivity) are needed to provide sufficient capacitance inever-smaller production-scale capacitor designs. Because of its highdielectric constant (or “k” value), titanium dioxide (TiO₂) is beingconsidered for use in non-volatile memory devices. TiO₂ has three maincrystalline phases: rutile, anatase, and brookite. The phase of a TiO₂crystal may depend on conditions of the TiO₂ growth process, such astemperature and method of deposition. Of significance in semiconductormanufacture is that the dielectric constant of TiO₂ varies based onproperties such as crystalline phase, orientation, and depositionmethod. For example, TiO₂ films grown on silicon substrates by atomiclayer deposition (ALD) generally have an anatase crystalline structure,which has a dielectric constant of about 30. The anatase TiO₂ may beconverted to rutile TiO₂ through an annealing process, including heatingthe TiO₂ to a temperature above 800° C.

Rutile TiO₂ may exhibit higher dielectric constants than anatase TiO₂.For example, along the c-axis of the rutile TiO₂, the dielectricconstant may be about 170, while the dielectric constant along thea-axis may be about 90. Dielectric constants above about 55 are neededto meet capacitance requirements of DRAM in size ranges currentlyproduced. As the scale of devices decreases, anatase TiO₂ is notgenerally useful because its dielectric constant is too low.

A high deposition or anneal temperature is generally required to formrutile TiO₂. For example, a semiconductor structure having anatase TiO₂thereon may be annealed by heating the anatase TiO₂ to a temperature ofabout 800° C. During the anneal, the TiO₂ crystalline structure maychange from anatase to rutile. However, heating the anatase TiO₂ to atemperature of about 800° C. may damage other structures on or withinthe semiconductor structure. For example, metal interconnects on or inthe semiconductor structure may melt under such conditions. Rutile TiO₂may also be formed directly (i.e., without annealing anatase TiO₂) bydeposition at high temperature. Because of the processing temperaturesneeded to form rutile TiO₂, use of rutile TiO₂ may be limited tosemiconductor structures that can tolerate high temperatures. DRAM andother structures may not withstand such temperatures. To take advantageof the high dielectric constants of rutile TiO₂ on semiconductorstructure that cannot tolerate high temperatures, it would be desirableto have a method of forming rutile TiO₂ without using high temperaturesrequired to deposit TiO₂ in the rutile phase and without annealinganatase TiO₂.

Japanese patent publication JP-A 2007-110111 describes a method offorming rutile TiO₂ on a ruthenium electrode using a process temperatureof less than 500° C. In that method, a ruthenium(IV) oxide pretreatmentfilm is formed by exposing a ruthenium electrode to gaseous ozone (O₃).Rutile TiO₂ is then deposited in a film over the ruthenium(IV) oxidefilm, and a second electrode is formed over both films.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A through 1C are schematics illustrating methods of formingrutile TiO₂ and semiconductor structures in accordance with embodimentsof the present disclosure; and

FIGS. 2A through 2D include X-ray diffraction (XRD) results showing theXRD response of semiconductor structures formed in accordance withembodiments of the present disclosure.

DETAILED DESCRIPTION

The following description provides specific details, such as materialtypes and processing conditions, in order to provide a thoroughdescription of embodiments of the present disclosure. However, a personof ordinary skill in the art will understand that the embodiments of thepresent disclosure may be practiced without employing these specificdetails. Indeed, the embodiments of the present disclosure may bepracticed in conjunction with conventional semiconductor fabricationtechniques employed in the industry. In addition, the descriptionprovided below does not form a complete process flow for manufacturing asemiconductor device, i.e., the semiconductor device structuresdescribed below do not form a complete semiconductor device. Only thoseprocess acts and structures necessary to understand the embodiments ofthe present disclosure are described in detail below. Additional acts toform a complete semiconductor device from the semiconductor devicestructures may be performed by conventional semiconductor fabricationtechniques, which are not described in detail herein.

Methods of forming rutile titanium dioxide (TiO₂) and methods of formingsemiconductor device structures having rutile TiO₂ are disclosed. Inparticular, the methods may be used to form a desired thickness ofrutile TiO₂. Rutile TiO₂ has a tetragonal crystal structure with acoordination number of six. Each titanium cation is surrounded by anoctahedron of six oxygen atoms. The methods may include oxidizing atransition metal to form a transition metal oxide, then forming rutileTiO₂ over the transition metal oxide. The rutile TiO₂ may be formed byALD. The transition metal oxide may be formed, for example, over asubstrate. The rutile TiO₂ may be formed at thicknesses of from about 30Å to about 200 Å, and may be formed from two or more precursors. Forexample, the rutile TiO₂ may be formed by ALD using a titanium halideprecursor and water, such as water vapor.

FIG. 1A shows a semiconductor structure 100 including a substrate 102over which metal 104 has been formed. The substrate 102 may be aconventional silicon substrate or other bulk substrate having a layer ofsemiconductor material. As used herein, the term “bulk substrate”includes not only silicon wafers, but also silicon-on-insulator (SOI)substrates, silicon-on-sapphire (SOS) substrates, epitaxial layers ofsilicon on a base semiconductor foundation, and other semiconductor oroptoelectronics materials, such as silicon-germanium, germanium, galliumarsenide, or indium phosphide. The substrate 102 may be in the form ofsemiconductor wafers, wafer fragments, or assemblies of such wafers orfragments. Substrate 102 may have other materials or features (notshown) formed upon or within the substrate 102 (e.g., electrodes, lines,vias, traces, sources, and drains). Such features may be formed byconventional semiconductor fabrication techniques, which are notdescribed in detail herein. By way of example, the substrate 102 may beformed from silicon, polysilicon, titanium nitride, an oxide, or ametal. The metal 104 may be formed on the substrate 102 by chemicalvapor deposition (CVD), ALD, physical vapor deposition (PVD), or anyother deposition method known in the art. The metal 104 may be formed ata thickness of from about 15 Å to about 100 Å, such as from about 30 Åto about 80 Å. The metal 104 may be any metal in which an oxide of themetal is configured to form a crystal structure similar to the crystalstructure of rutile TiO₂. The metal 104 may be a transition metal, suchas vanadium (V), chromium (Cr), tungsten (W), manganese (Mn), ruthenium(Ru), osmium (Os), rhodium (Rh), iridium (Ir), platinum (Pt), germanium(Ge), tin (Sn), or lead (Pb). In one embodiment, the metal 104 is Ru.Though not shown in FIG. 1A, an adhesion material may, optionally, beformed on the substrate 102 to promote adhesion of the metal 104 to thesubstrate 102. Adhesion materials are known in the art and, therefore,are not described in detail herein.

The metal 104 may be oxidized with an oxidant, for example, by exposingthe semiconductor structure 100 to the oxidant. A portion of the metal104 may react with the oxidant to form the metal oxide 106, shown onsemiconductor structure 100′ in FIG. 1B. The oxidant may be an oxidizerthat is of sufficient strength to react with the metal 104 to form ametal oxide 106. However, the strength of the oxidizer may not be suchas to substantially remove (i.e., etch) the metal 104.

The oxidant may be, for example, oxygen (O₂), nitric oxide (NO), nitrousoxide (N₂O), etc. The oxidant may be substantially pure (i.e., greaterthan about 95% pure, such as greater than about 99% pure or greater thanabout 99.9% pure), or may be mixed with an inert gas (e.g., argon,nitrogen). During the oxidation, absolute pressure within a chamber (notshown) in which the oxidation is conducted may be maintained at apressure from about 13 Pa (about 0.1 Ton) to about 101.3 kPa (about 760Torr). During the oxidation, the semiconductor structure 100 may beheated to a temperature of, for example, from about 150° C. to about450° C., such as from about 200° C. to about 400° C., or from about 250°C. to about 350° C. The semiconductor structure 100 may be heated in thepresence of the oxidant for a time period of from about 30 seconds toabout 60 minutes, such as a time period of from about 5 minutes to about20 minutes.

During the oxidation, strong oxidants, such as ozone (O₃), may beavoided, because the strong oxidant may remove at least a portion of themetal 104. For example, if ruthenium is used as the metal 104, theruthenium may react with ozone to form RuO₄, which is volatile. Thevolatile RuO₄ may vaporize, leaving little or no ruthenium on thesemiconductor structure 100′. Since the metal 104 may have a thicknessof less than about 100 Å, removing even a portion of metal 104 may makethe metal 104 too thin for effective formation of metal oxide 106 andsubsequent formation of the rutile TiO₂ thereon.

The metal oxide 106 formed on the metal 104 may have a thickness of fromabout 5 Å to about 10 Å. In one embodiment, the metal oxide 106 is about7 Å thick. The metal oxide 106 may be a material having a crystallinestructure similar to the crystalline structure of rutile TiO₂, forexample, VO₂, CrO₂, WO₂, MnO₂, RuO₂, OsO₂, RhO₂, IrO₂, PtO₂, GeO₂, SnO₂,or PbO₂. In one embodiment, the metal oxide 106 is ruthenium(IV) oxide(RuO₂).

Referring now to semiconductor structure 100″ shown in FIG. 1C, rutileTiO₂ 108 may be formed over the metal oxide 106. The rutile TiO₂ 108 maybe formed by an ALD process that includes sequentially exposing thesemiconductor structure 100′ to gaseous precursors suitable for use asALD precursors. The ALD precursors may include a titanium halide (TiX₄)precursor, where “X” is a halide, such as fluorine (F), chlorine (Cl),bromine (Br), or iodine (I), and water (H₂O), such as water vapor. Thetitanium halide precursor may be, for example, titanium tetrafluoride(TiF₄), titanium tetrachloride (TiCl₄), titanium tetrabromide (TiBr₄),or titanium tetraiodide (TiI₄). The rutile TiO₂ 108 may be formed bysequentially exposing the semiconductor structure 100′ to each ALDprecursor in a chamber (not shown), such as an ALD chamber. Chambers foruse in ALD processes are known in the art and, therefore, details ofsuch are not described herein. The chamber may be maintained at atemperature, for example, of from about 150° C. to about 600° C., suchas a temperature from about 150° C. to about 450° C. Though formation ata higher temperature may also produce rutile TiO₂, the surface of rutileTiO₂ formed at a higher temperature may be too rough for use in someapplications. Furthermore, some semiconductor structures 100′ may nottolerate exposure to a higher temperature. The rutile TiO₂ 108 may beformed to a selected thickness, such as from about 5 Å to about 200 Å.By forming the rutile TiO₂ 108 by ALD, the thickness of the rutile TiO₂108 may depend on the number of titanium and oxygen monolayersdeposited. That is, the rutile TiO₂ 108 of a selected thickness may beachieved by selecting an appropriate number of ALD cycles.

The crystalline structure of the metal oxide 106 may enable the TiO₂ toform in the rutile phase at a lower temperature than those temperaturesconventionally utilized for the formation of rutile TiO₂. For example,anatase TiO₂ is, conventionally, heated to a temperature above 800° C.to form rutile TiO₂. However, in the methods according to embodiments ofthe present disclosure, the formation of rutile TiO₂ 108 over the metaloxide 106 may be achieved at a substantially lower temperature (e.g., atemperature of less than about 600° C.). Without being bound by aparticular theory, it is believed that crystalline molecular sites on asurface of the metal oxide 106 may guide titanium atoms into positionsthat correspond with the positions of titanium atoms in a rutile TiO₂crystalline structure. With the initial titanium atoms in place for arutile crystalline structure, the oxygen atoms may arrange inappropriate positions to continue growth of the rutile crystallinestructure. In other words, the metal oxide 106 may act as a template forforming the rutile TiO₂ 108. Therefore, metal oxides 106 having acrystalline structure similar to rutile TiO₂ may be better suited toforming rutile TiO₂ 108 thereupon than metal oxides 106 withless-similar crystal structures. The rutile TiO₂ 108 may be formed to adesired thickness, such as to a thickness of from about 30 Å to about200 Å, by repeating the ALD process until a desired number of ALD cycleshas been conducted.

Once an initial portion of the rutile TiO₂ has been formed as describedabove, an additional portion of rutile TiO₂ 108′ may, optionally, beformed over the rutile TiO₂ 108 as indicated by the dashed line in FIG.1C. This rutile TiO₂ 108′ may be formed by ALD as described above andmay be formed in the same chamber or in a different chamber.Alternatively, after the rutile TiO₂ 108 has been formed by the ALDprocess using TiX₄ and H₂O as ALD precursors, rutile TiO₂ 108′ may beformed using a TiX₄ precursor and a different oxygen-containingprecursor, such as an oxygen-containing precursor having an increasedoxidizing strength compared to H₂O. For example, ozone (O₃) may be usedas the oxygen-containing precursor. The oxygen-containing precursor,which has increased oxidizing strength compared to H₂O, may not besuitable as an ALD precursor for forming the rutile TiO₂ 108 directly onthe metal oxide 106 because the oxygen-containing precursor may damageor remove (e.g., etch) the metal oxide 106. But, if the metal oxide 106is protected by rutile TiO₂ 108 (e.g., a rutile TiO₂ 108 having athickness of at least about 5 Å), the oxygen-containing precursor maynot react with the metal oxide 106. For example, without the protectionprovided by rutile TiO₂ 108, exposure of ruthenium or ruthenium(IV)oxide to ozone may produce ruthenium tetraoxide (RuO₄), which is avolatile compound. In this situation, the RuO₄ (metal oxide 104) mayvaporize, leaving no rutile crystalline structure appropriate forforming rutile TiO₂ 108 thereon. But, once an initial portion of rutileTiO₂ 108 has been formed over the metal oxide 106, the possibility offurther oxidation (and, therefore, loss) of metal oxide 106 maydiminish. The rutile TiO₂ 108′ may be formed at any selected thickness,such as from about 30 Å to about 200 Å. Rutile TiO₂ 108′ of a selectedthickness may be formed by selecting an appropriate number of ALDcycles. After formation of the rutile TiO₂ 108′, the rutile TiO₂ 108′may be indistinguishable from rutile TiO₂ 108 (i.e., there may be nodetectable difference or interface between rutile TiO₂ 108 and rutileTiO₂ 108′).

The rutile TiO₂ 108 formed by the methods according to embodiments ofthe present disclosure may be used as an insulator in a capacitor, suchas a metal-insulator-metal capacitor of a DRAM memory device or a NANDmemory device. Additional fabrication acts for forming themetal-insulator-metal capacitor and the DRAM or NAND memory device areknown in the art and, therefore, details of such are not providedherein.

The formation of rutile TiO₂ by methods according to embodiments of thepresent disclosure was confirmed by X-ray diffraction (XRD) of asemiconductor structure similar to semiconductor structure 100″. FIG. 2Ashows the results of the XRD analysis on a semiconductor structure 100′similar to that shown in FIG. 1B. The semiconductor structure 100′included a silicon substrate 102, ruthenium as metal 104, and rutheniumoxide as metal oxide 106. The semiconductor structure 100′ was formed byapplying Ru to the silicon substrate by a CVD process. The Ru wasoxidized at a temperature of 250° C. for 10 minutes in a mixture of 30%O₂ and 70% Ar, at a chamber pressure of 133 Pa (1.0 Ton), producing RuO₂on the Ru. The semiconductor structure 100′ was then analyzed by grazingincidence X-ray diffraction (GI-XRD). FIG. 2A shows peaks at measuredangles (2θ) of about 38.5° and 44°, which correspond to known rutheniumresponses.

FIG. 2B shows the XRD results of a semiconductor structure similar tothe semiconductor structure 100″ shown in FIG. 1C. Rutile TiO₂ wasformed by ALD on the semiconductor structure 100′ tested in FIG. 2Ausing TiCl₄ and H₂O as ALD precursors, forming semiconductor structure100″. The semiconductor structure 100′ was exposed to each precursor 220times, in series, at 400° C. The semiconductor structure 100″ was thensubjected to XRD analysis. The graph in FIG. 2B shows peaks at measuredangles (2θ) of about 27.5°, 38.5°, 42.5°, and 44°. The peaks at 38.5°,42.5°, and 44° correspond to known ruthenium responses. The peak at27.5° corresponds to a known rutile TiO₂ response, and its presenceindicates that rutile TiO₂ was formed over the RuO₂.

For comparison, FIGS. 2C and 2D show XRD results of semiconductorstructures similar to the semiconductor structure 100″ except that theTiO₂ was formed using non-halide titanium precursors (i.e., titaniumoxide precursors). FIG. 2C shows the XRD results of a semiconductorstructure formed by ALD TiO₂ deposition using CH₃C₅H₄Ti[N(CH₃)₂]₃(TIMCTA) as the titanium precursor. Two semiconductor structures weretested having Ru and RuO₂ applied as described with respect to FIGS. 2Aand 2B. Curve 1 in FIG. 2C shows the intensity of diffracted X-rays on asemiconductor structure having 100 Å thick TiO₂ formed by ALD usingTIMCTA and H₂O as the ALD precursors. As shown in FIG. 2C, rutile TiO₂was not formed on the substrate (i.e., the 27.5° rutile peak, as seen inFIG. 2B, was not observed). The response curve showed only the Ru peaksat 38.5°, 42.5°, and 44°. Absence of the rutile peak indicates thatrutile TiO₂ was not present in significant amount on the substratealigned under these conditions.

Curve 2 in FIG. 2C shows the intensity of diffracted X-rays on asemiconductor structure having TiO₂ formed with two sets of ALDprecursors. The semiconductor structure included Ru and RuO₂ asdescribed above. A 30 Å layer of TiO₂ was formed using TIMCTA and H₂O asthe ALD precursors, and a 70 Å layer of TiO₂ was formed over the 30 Ålayer using TIMCTA and O₃ as the ALD precursors. XRD analysis of thissemiconductor structure produced the peaks for Ru, plus a peak near 25°,indicating that anatase phase TiO₂ was formed on the semiconductorstructure (see curve 2). The 27.5° rutile peak (as shown in FIG. 2B) wasnot observed, indicating that rutile TiO₂ was not present in asignificant amount on the semiconductor structure formed under theseconditions.

FIG. 2D shows the XRD results for a semiconductor structure formed byALD TiO₂ deposition using titanium tetraisopropoxide (Ti(OC₃H₇)₄ orTTIP) and H₂O as the ALD precursors. The semiconductor structureincluded Ru and RuO₂ as described above, and the TiO₂ was formedthereover. The XRD analysis showed a ruthenium peak at about 44.5°, pluspeaks at about 25.5° for anatase TiO₂, and at about 27.5° for rutileTiO₂. The presence of both anatase and rutile TiO₂ peaks suggests thatformation of ALD TiO₂ with TTIP did not produce a uniform rutile TiO₂phase under these conditions.

CONCLUSION

In one embodiment, the present disclosure includes a method of formingrutile titanium dioxide. The method comprises exposing a transitionmetal to oxygen gas (O₂) to produce an oxidized transition metal andforming rutile titanium dioxide over the oxidized transition metal.

In another embodiment, the present disclosure includes a method offorming rutile titanium dioxide. The method comprises oxidizing aportion of a ruthenium material to ruthenium(IV) oxide, introducing agaseous titanium halide precursor and water vapor to the ruthenium(IV)oxide, and forming rutile titanium dioxide on the ruthenium(IV) oxide.

In yet another embodiment, the present disclosure includes a method offorming a semiconductor structure that comprises forming ruthenium on asubstrate, exposing the ruthenium to oxygen gas (O₂) to oxidize aportion of the ruthenium to ruthenium(IV) oxide, and exposing theruthenium(IV) oxide to titanium tetrachloride and water to form rutiletitanium dioxide on the ruthenium(IV) oxide.

While the invention is susceptible to various modifications andalternative forms, specific embodiments have been shown, by way ofexample, in the drawings and have been described in detail herein.However, the invention is not intended to be limited to the particularforms disclosed. Rather, the invention is to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the following appended claims and their legal equivalents.

What is claimed is:
 1. A method of forming a semiconductor structure,comprising: forming ruthenium on a substrate; exposing the ruthenium tooxygen gas (O₂) to oxidize a portion of the ruthenium to formruthenium(IV) oxide overlying a remaining portion of the rutheniumwithout etching the ruthenium; and exposing the ruthenium(IV) oxide totitanium tetrachloride and water to form rutile titanium dioxide on theruthenium(IV) oxide by atomic layer deposition.
 2. The method of claim1, wherein exposing the ruthenium to O₂ to oxidize a portion of theruthenium to form ruthenium(IV) oxide comprises forming ruthenium(IV)oxide having a thickness of from about 5 Å to about 10 Å.
 3. The methodof claim 1, wherein exposing the ruthenium to O₂ to oxidize a portion ofthe ruthenium to form ruthenium(IV) oxide comprises exposing theruthenium to the O₂ at a temperature of from about 200° C. to about 400°C.
 4. The method of claim 1, wherein exposing the ruthenium(IV) oxide totitanium tetrachloride and water to form rutile titanium dioxide on theruthenium(IV) oxide comprises exposing the ruthenium(IV) oxide totitanium tetrachloride and water while maintaining the substrate at atemperature below about 450° C.
 5. The method of claim 1, furthercomprising exposing the rutile titanium dioxide to titaniumtetrachloride and ozone.
 6. The method of claim 1, wherein exposing theruthenium to O₂ to oxidize a portion of the ruthenium to form ruthenium(IV) oxide comprises exposing ruthenium having a thickness of from about15 Å to about 100 Å to the O₂.
 7. The method of claim 1, furthercomprising forming additional rutile titanium dioxide on the rutiletitanium dioxide by sequentially exposing the rutile titanium dioxide toa titanium halide precursor and another oxidizer.
 8. The method of claim7, wherein sequentially exposing the rutile titanium dioxide to atitanium halide precursor and another oxidizer comprises exposing therutile titanium dioxide to the titanium halide precursor and ozone.